Normalize by Area Under Curve

step_measure_normalize_auc() creates a specification of a recipe step that divides each spectrum by its area under the curve (computed using trapezoidal integration). This is useful for chromatography where peak areas are meaningful.

Usage

step_measure_normalize_auc(
  recipe,
  measures = NULL,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("measure_normalize_auc")
)

Arguments

recipe

A recipe object. The step will be added to the sequence of operations for this recipe.

measures

An optional character vector of measure column names to process. If NULL (the default), all measure columns (columns with class measure_list) will be processed. Use this to limit processing to specific measure columns when working with multiple measurement types.

role

Not used by this step since no new variables are created.

trained

A logical to indicate if the quantities for preprocessing have been estimated.

skip

A logical. Should the step be skipped when the recipe is baked by recipes::bake()? While all operations are baked when recipes::prep() is run, some operations may not be able to be conducted on new data (e.g. processing the outcome variable(s)). Care should be taken when using skip = TRUE as it may affect the computations for subsequent operations.

id

A character string that is unique to this step to identify it.

Value

An updated version of recipe with the new step added to the sequence of any existing operations.

Details

The area under the curve is computed using trapezoidal integration:

$$AUC = \sum_{i=1}^{n-1} \frac{(y_i + y_{i+1})}{2} \cdot (x_{i+1} - x_i)$$

where \(y\) are the values and \(x\) are the locations.

After transformation, the AUC of each spectrum will equal 1.

If the AUC is zero or NA, a warning is issued and the original values are returned unchanged. At least 2 points are required for integration.

No selectors should be supplied to this step function. The data should be in the internal format produced by step_measure_input_wide() or step_measure_input_long().

See also

step_measure_normalize_sum(), step_measure_normalize_peak()

Other measure-normalization: step_measure_normalize_max(), step_measure_normalize_peak(), step_measure_normalize_range(), step_measure_normalize_sum(), step_measure_normalize_vector()

Examples

library(recipes)

rec <-
  recipe(water + fat + protein ~ ., data = meats_long) |>
  update_role(id, new_role = "id") |>
  step_measure_input_long(transmittance, location = vars(channel)) |>
  step_measure_normalize_auc() |>
  prep()

bake(rec, new_data = NULL)
#> # A tibble: 215 × 5
#>       id water   fat protein .measures
#>    <int> <dbl> <dbl>   <dbl>    <meas>
#>  1     1  60.5  22.5    16.7 [100 × 2]
#>  2     2  46    40.1    13.5 [100 × 2]
#>  3     3  71     8.4    20.5 [100 × 2]
#>  4     4  72.8   5.9    20.7 [100 × 2]
#>  5     5  58.3  25.5    15.5 [100 × 2]
#>  6     6  44    42.7    13.7 [100 × 2]
#>  7     7  44    42.7    13.7 [100 × 2]
#>  8     8  69.3  10.6    19.3 [100 × 2]
#>  9     9  61.4  19.9    17.7 [100 × 2]
#> 10    10  61.4  19.9    17.7 [100 × 2]
#> # ℹ 205 more rows